In a current long term evolution (LTE) system, a media access control (MAC) layer is responsible for multiplexing multiple different RLC protocol data packet units (PDU) (RLC PDUs) of a radio link control (RLC) layer into an MAC layer PDU (MAC PDU), and then transmits on an air interface, wherein one RLC entity corresponds to one logical channel, and the RLC PDU is also called an MAC service data unit (SDU). The RLC PDU of different logical channels is expressed by a logical channel identification (LCID) in an MAC PDU header. Only after receiving the MAC PDU correctly, the MAC layer of a receiving end may deliver the MAC SDU of the different logical channels to RLC layer entities corresponding to the logical channels according to the LCID in the MAC PDU header. If the MAC layer does not receive the MAC PDU correctly, a sending end is firstly required to perform hybrid automatic repeat request (HARQ) retransmission in general until the MAC PDU is successfully received, or the MAC PDU is discarded after reaching a certain number of retransmissions.
Besides the above-mentioned operations of the MAC layer, the RLC layer also performs retransmission or not according to different transmission modes. That is, if the RLC layer is in an acknowledgement mode (AM), when the MAC layer still unsuccessfully receives the MAC PDU by means of the HARQ retransmission, automatic repeat request (ARQ) retransmission may be performed on the MAC SDU (i.e., RLC PDU) contained in the unsuccessfully received MAC PDU at the RLC layer. After successfully receiving the RLC PDU, the RLC layer of the receiving end recombines the RLC PDU into an RLC SDU and sequentially delivers the RLC SDU to an upper protocol stack of the RLC layer in a lossless manner, the upper protocol stack of the RLC layer may be a packet data convergence protocol (PDCP) layer, at this time, the RLC SDU is also called a PDCP PDU, in addition, the upper protocol stack of the RLC layer may also be radio resource control (RRC) or the like. If the RLC layer still fails to successfully receive the RLC PDU after a maximum retransmission limit, the link is considered to have a problem, and link failure information will be reported to a radio resource control (RRC) layer, in order to trigger RRC connection reestablishment. An RLC layer in an unacknowledgement mode (UM) only depends on the HARQ retransmission of the MAC layer, the RLC layer itself does not perform retransmission, so after the MAC layer discards the MAC PDU, the MAC SDU (i.e., RLC PDU) contained in the discarded MAC PDU could not be recombined into the RLC SDU (i.e., PDCP PDU), at this time, the RLC layer may only guarantee to sequentially deliver the RLC SDU (i.e., PDCP PDU) to the upper layer protocol stack and could not guarantee non-loss. In addition, the RLC layer will segment or cascade the RLC SDU (i.e., high level PDU, such as PDCP PDU) according to the sizes of low level (e.g., the MAC layer) resources, in order to be adapted to the low level resources.
However, a problem that an air interface resource is wasted exists in the prior art.